The present technology relates to a memory element and a memory apparatus that have a plurality of magnetic layers and make a record using a spin torque magnetization switching.
Along with a rapid development of various information apparatuses from mobile terminals to large capacity servers, further high performance improvements such as higher integration, increases in speed, and lower power consumption have been pursued in elements such as a memory element and a logic element configuring the apparatuses.
In particular, a semiconductor non-volatile memory has significantly progressed, and, as a large capacity file memory, flash memory is spreading at such a rate that hard disk drivers are replaced with the flash memory.
Meanwhile, the development of a semiconductor non-volatile memory has progressed as a substitute for the current NOR flash memory, DRAM or the like in general use, in order to use them for code storage or as a working memory. Examples include FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetic Random Access Memory), PCRAM (Phase-Change Random Access Memory), or the like. A part of these is already in practical use.
Among these non-volatile memories, the MRAM performs the data storage using a magnetization direction of a magnetic material so that high speed and nearly unlimited (1015 times or more) rewriting can be made, and therefore the MRAM has already been used in fields such as industrial automation and an airplane.
The MRAM has been expected to be expanded to code storage or working memory in the near future due to the high-speed operation and reliability.
However, the MRAM has challenges related to lowering power consumption and increasing capacity.
This is a basic problem caused by the recording principle of MRAM, that is, the method of switching the magnetization using a current magnetic field generated from an interconnection.
As a method of solving this problem, a recording method not using the current magnetic field (that is, a magnetization switching method) is under review. In particular, research on a spin torque magnetization switching has been actively made (for example, see Japanese Unexamined Patent Application Publication No. 2003-17782 and U.S. Pat. No. 5,695,864).
The memory element using a spin torque magnetization switching includes an MTJ (Magnetic Tunnel Junction) similarly as the MRAM.
This uses a phenomenon in which, when spin-polarized electrons passing through a magnetic layer which is fixed in an arbitrary direction enter another free (the direction is not fixed) magnetic layer, a torque is applied to the magnetic layer, and the free magnetic layer (the memory layer) is switched when a current having a predetermined threshold value or more flows. The rewriting of 0/1 is performed by changing the polarity of the current.
An absolute value of a current for the switching of the free magnetic layer is 1 mA or less in the case of a memory element with a scale of approximately 0.1 μm. In addition, since this current value decreases in proportion to a volume of the memory element, scaling is possible.
In addition, since a word line necessary for the generation of a recording current magnetic field in the MRAM is not necessary, there is an advantage that a cell structure becomes simple.
Hereinafter, the MRAM utilizing a spin torque magnetization switching will be referred to as a Spin Transfer Torque-Magnetic Random Access Memory (STT-MRAM).
Great expectations are put on the STT-MRAM as a non-volatile memory capable of realizing lower power-consumption and larger capacity while maintaining the advantages of the MRAM in which high speed and nearly unlimited rewriting may be performed.